Aging of optical properties of polished copper mirrors

Effects of aging on optical properties of polished copper mirrors were studied; data are referable to wavelengths 10.6 and 0.63 microns. Reflectivity and total integrated scatter of copper mirrors subjected to different processing histories were measured using fringes of equal chromatic order. Constancy of the properties investigated was checked in three aging experiments, to eliminate degradation occurring before the first measurements. While growth of visible oxide is noted, the reflectivity of the specimens did not degrade by more than 0.005 at 10.6 microns, or more than 0.02 at 0.63 micron, while TIS variation remained within 20%. This argues in favor of the use of copper without protective coatings in 10.6 micron laser applications (where 1% absorption is acceptable).